The present invention relates to an apparatus and method for securing body parts with a surgical cable. In particular, the invention relates to a surgical cable assembly that includes a flexible cable that can be wrapped around body parts, such as bones, and a rotating crimpable coupling for securing the flexible cable in a closed loop about the bone.
Surgical cables are used in various surgical procedures, for example, to fix fractured bones or to secure an implant to a bone. The cable may be a monofilament wire or multifilament cable. Typically, the cable is used to encircle the broken bone and hold it together as it heals or to hold an implant device in position next to a bone.
The configuration of the surgical cable assembly may impact the ease with which the cable is installed. A typical surgical cable assembly may include the cable and one or more pieces for securing the cable in a loop under tension, such as a stop to fix the ends of the cable to form the tensioned loop. One known type of cable assembly utilizes a small, permanent loop at one end, formed by a first crimp member. The opposite free end of the cable is wrapped around the bone and threaded through the small loop during the surgical procedure. The resulting second loop formed around the bone is then secured by sliding a loose tubular crimp member along the cable to the small permanent loop and crimping the tubular member with a crimping tool. Examples of such assemblies are disclosed in U.S. Pat. Nos. 4,966,600 and 5,116,340.
Given the need to limit the intrusiveness of the cable assembly within the surgical site and the desire to limit the size of the incision, such cable assemblies and associated components tend to be small and therefore difficult for a surgeon to handle. In particular, the task of threading the cable through the aperture in the small loose tubular member during surgery may be difficult for a surgeon wearing gloves. Further, the requirement that the surgeon account for all items used during surgery makes the use of small, loose pieces that may be readily dropped undesirable.
Installation of surgical cables may be frustrated by factors such as the difficulties encountered by the surgeon in having to handle the various devices and implements required for installation of a cable assembly. For example, one or more tools to tension the cable and/or temporarily hold the cable, to crimp the cable crimp, and to cut the cable may be used during installation of the surgical cable. The surgeon must be able to manipulate these various tools while installing the cable assembly. The physical constraints of the surgical site also may impact the ease with which a surgical cable assembly is installed. Access to the surgical site may be obstructed due to the particular location of the body where the cable is being installed or may be limited as a result of the desire to limit the size of the incision. Thus, the surgeon may experience difficulties in working with a number of tools in a small area while trying to position, tighten and fix the cable assembly about the bone, such that it may not be possible to readily achieve the desired tension and effectively maintain it until the cable is secured.
Another type of cable assembly is secured by a single L-shaped crimp member having two crimp able portions. One end portion of the cable is immovably fixed in the first crimp able portion. The opposite end of the cable is threaded around the bone and then fixed in the second crimp able portion. With this assembly, the surgeon does not have to handle a separate, loose crimp member. To form the cable loop, the surgeon only has to thread the opposite end of the cable through a second aperture in the crimp. Such an assembly is disclosed in U.S. Pat. No. 5,423,820 to Miller, et al.
When installing a cable assembly, it is desirable to obtain a predetermined amount of tension in the cable loop so that the cable is properly mechanically fixed around the bone. It is thus important to avoid formation of slack in the loop as the surgical installation is being completed. To limit slack, it is desirable to tighten the cable so that the cable generally conforms to the shape of the bone and fits snugly around the bone. The strength of a cable loop is also greater when the two ends of the cable are positioned essentially parallel to one another in a plane tangent to the surface of the bone. Because the ends of the cable disclosed in Miller, et al. are oriented perpendicular to one another as a result of the configuration of the L-shaped crimp, it may not be possible to have both ends flush with the surface of the bone. With both cable ends in the Miller, et al. assembly fixed in the L-shaped crimp, the crimp cannot rotate or pivot in any direction without forming sharp bends in the cable. Moreover, the L-shaped crimp of Miller, et al. may protrude into adjacent tissue and cause the cable loop to be lifted away from the bone along a length of the loop which also may reduce its strength.
U.S. Pat. Nos. 5,928,237 and 5,569,253 disclose cable assemblies utilizing two crimps, the crimps being held in ball and socket or ball and seat abutment to allow them to swivel relative to each other. One drawback of these assemblies is the complex machining required to fabricate the relatively small ball and socket or ball and seat joints. A further drawback is that in use, the swivel action of the joint may prevent holding the cable loop roughly in a single plane and result in twisting and bending of the cable. The swivel action between the crimps may also make the task of locating the second crimp aperture and threading the free cable end through the crimp aperture difficult during surgery.
Thus it is desirable to have a surgical cable assembly that may be readily handled by a surgeon and easily installed during surgery to form a secure cable loop about a bone. It is also desirable to have such a surgical cable assembly that may be orientated to facilitate tensioning of the loop to avoid formation of slack, cable twisting, and sharp cable bends. The cable assembly should be easy to manufacture, compact, and only minimally intrusive in the body.
In accordance with the present invention, an apparatus and method are provided for securing body parts, such as bones. A surgical cable assembly for encircling a bone comprises a length of cable that has first and second ends and a coupling member which has a shoulder portion having a first aperture extending therethrough. A small, preformed loop near the first end of the cable has a portion loosely received in the shoulder aperture. The coupling member also has a second part, or neck portion. The neck portion has a second aperture extending through a malleable portion configured to be crimped about the flexible cable for fixing the coupling along the flexible cable so as to secure the surgical cable assembly around the bone.
The portion of cable extending through the shoulder aperture forms an axis of rotation for the coupling member. With the coupling member rotatably mounted about a portion of the small cable loop, the second end of the flexible cable is passable through the second aperture to loop the flexible cable around the bone at a desired orientation. Because the small loop adjacent the first cable end is not fixed (i.e., crimped) in the shoulder aperture, the angle of the neck portion of the coupling member relative to the bone surface may be adjusted to achieve the desired tension, strength and orientation of the cable assembly around the bone by pivoting the coupling member about the preformed loop. Once the cable is looped around the bone, the neck of the coupling member is fixed at a position along the flexible cable by crimping to maintain a predetermined tension of the loop and secure the loop in a desired position around the bone.
A separate loop crimp member secures the first end of the flexible cable back along the length of the flexible cable to form the small, permanent loop adjacent the first end of the flexible cable. The flexible cable is rotatably attached to the first part through the first aperture by the connecting loop. The coupling member may also comprise a flange for controlling the degree of rotation of the coupling member around the small preformed loop.
A method of securing a bone with a surgical cable assembly includes first providing a surgical cable assembly that comprises a coupling member having a shoulder portion with a first aperture extending therethrough, a neck portion having a second aperture extending therethrough, and a flexible cable having first and second ends spaced by a length, where the coupling member is rotatably mounted on a small cable loop adjacent the first end by means of the first aperture.
The method further comprises passing the second end of the flexible cable around the bone and through the second aperture of the coupling member to form a loop of the flexible cable around the bone. The loop is then tightened to a desired tension about the bone. A suitable tensioning tool may be used for this purpose. Depending on the contour of the bone surface and the desired tension, the tensioning step may involve pivoting the coupling member relative to the small loop threaded through the first aperture.
The neck of the coupling member is crimped to secure it about the flexible cable at a point along the cable length necessary to maintain the desired loop tension and desired angle of the neck of the coupling member relative to the bone surface. After the coupling member is crimped, the flexible cable is cut essentially flush with the end of the neck portion, at the end opposite the cable loop.
In the preferred method, the coupling member is provided pre-mounted on the small cable loop by passing the first cable end through the first aperture of the coupling and then securing it back against a length of the flexible cable so as to form the small loop. A separate tubular member is crimped about the first end of the flexible cable and the length of flexible cable along which the end is doubled back so as to fix the first end and form the preformed loop.
The method also may include passing the flexible cable around a medical implant or graft positioned adjacent the bone in order to secure the medical implant or graft against the bone.